T-DM1 is an experimental targeted therapy medicine that's a combination of Herceptin (chemical name: trastuzumab) and a chemotherapy medicine called maytansine.
A small, preliminary research study found that women diagnosed with HER2-positive locally advanced or metastatic breast cancer and treated with T-DM1 lived longer without the cancer showing signs of progression compared to similar women who received a standard treatment combination of Herceptin and the chemotherapy Taxotere (chemical name: docetaxel). The results were presented at the September 2011 European Multidisciplinary Cancer Conference (ECCO-ESMO) annual meeting.
Locally advanced breast cancer is breast cancer that has spread to tissue near the breast, but not to parts of the body away from the breast. Metastatic breast cancer is advanced-stage cancer that has spread to parts of the body away from the breast -- the bones, liver, or brain, for example.
Herceptin is a targeted therapy medicine used to treat advanced-stage, HER2-positive breast cancers and to lower the risk of recurrence of early-stage, HER2-positive breast cancer that has a high risk of recurrence. HER2-positive cancers make too much of the HER2 protein. The HER2 protein sits on the surface of cancer cells and receives signals that tell the cancer to grow and spread. About one out of every four breast cancers is HER2-positive. Herceptin works by attaching to the HER2 protein and blocking it from receiving growth signals.
Maytansine, like some other chemotherapy medicines, disrupts the way cells grow. Maytansine on its own isn't considered a targeted medicine, which means it can affect healthy cells as well as cancer cells.
T-DM1 was designed to deliver maytansine to cancer cells in a targeted way by attaching the maytansine to the Herceptin. Herceptin then carries the maytansine to the HER2-positive cancer cells.
137 women who had been diagnosed with locally advanced or metastatic HER2-positive breast cancer participated in the study reviewed here. None of them had been previously treated with either targeted therapy or chemotherapy before participating in the study. Half of the women were treated with T-DM1. The other half were treated with Herceptin and Taxotere.
The researchers found that the women who were treated with T-DM1 had an average of a little over 14 months pass before the cancer showed signs of progression (called progression-free survival), compared to only a little over 9 months for the women who received Herceptin and Taxotere, the standard treatment. Still, the numbers of women whose cancer showed signs of weakening while on treatment (called objective response) were the same regardless of which treatment a woman received.
The researchers did find that significant treatment side effects were nearly twice as likely (89.4%) in the women who received the standard combination compared to the women who received T-DM1 (46.4%). Taxotere in the standard treatment combination accounted for many of the serious treatment side effects. As a result, more women (28.8%) treated with the standard combination had to stop therapy because of those side effects compared to the women treated with T-DM1 (7.2%).
Because of the improvement in progression-free survival and the lower likelihood of needing to stop treatment because of side effects, the average time before treatment had to be stopped or changed was longer (10 months) among the women treated with T-DM1 compared to the women treated with Herceptin and Taxotere (5.5 months).
Findings from other preliminary research also suggest that T-DM1 could prove to be a useful treatment for advanced breast cancer. Still, more research involving larger numbers of women is needed before doctors can be sure whether, when, and in whom T-DM1 should be used to treat breast cancer.
If you're being treated for advanced-stage, HER2-positive breast cancer, you and your doctor may be considering a number of treatment options, especially if the cancer has stopped responding to standard treatments. If you're willing to participate in a clinical trial, you may have even more options available, possibly including experimental treatments such as T-DM1. Talk to your doctor about clinical trials that might be a good fit for you and your unique situation. Visit the Breastcancer.org Clinical Trials pages to learn more.